This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Heavy metal uptake in plants is an important research area not only in the sense of basic research, but also because of its impact on human nutrition and its application for the phytoremediation of contaminated soils. For the latter task, as well as for the commercial extraction of metals from naturally metal-rich soils that are, however, unsuitable for conventional mining operations, hyperaccumulator plants are of primary importance. These plants are able to accumulate several percent of metals in the dry mass of their above-ground parts;the unusual physiology of these plants is a topic of intensive worldwide research efforts. One of the presently most interesting topics in this area of research are the biochemistry and biophysics of transporters that lead metal from the roots to their final storage site in the shoot. In the current project we successfully purified a Cd/Zn ATPase (TcHMA4) from hyperaccumulator roots in its native state (Parameswaran et al., 2007) and we now want to further investigate which ligands in TcHMA4 bind metal (in this case cadmium). The protein belongs to the P1B-type ATPases that are present in humans as well and several members of this family of pumps are involved in important diseases like the Menkes and Wilsons diseases that are caused by mutation in copper ATPases. While the genes are known, only little is known about biochemistry and biophysics of P1B-type ATPases as the purification is difficult to achieve.